(1) Field of the Invention
The present invention relates to high ratio speed reducers, and, more particularly, the present invention relates to a speed reducer of the type employing a double chain engaging an orbiting drive sprocket and an output sprocket.
(2) Description of the Prior Art
Speed reducing mechanisms having drive and output sprockets engaging an endless double chain are known. One type of speed reducing mechanism is disclosed in U.S. Pat. No. 3,307,474 wherein the output sprocket has a number of teeth all engaging the double chain. The drive sprocket, which has fewer teeth than the output sprocket, orbits on an eccentric crank portion of an input shaft through a circular path having a diameter equal to the diameter of the output sprocket. In the patent it is recognized that it is desirable to have as many teeth on the drive sprocket as possible while still providing a minimal amount of clearance between the non-aligned disengaged teeth of the drive sprocket and the endless double chain. In one example given in this patent, the larger diameter output sprocket has thirty-five teeth and the drive sprocket has thirty-two teeth to provide minimum clearance between the disengaged teeth and the endless double chain.
U.S. Pat. No. 3,094,885 and U.S. Pat. No. 3,726,158 disclose similar speed reducing mechanisms having an orbiting drive sprocket and an output sprocket operatively coupled by an endless double chain.
It is an object of the present invention to provide a speed reducer wherein the number of teeth on the output sprocket differs by as few as one tooth from the number of drive sprocket teeth and clearance between the non-aligned disengaged drive sprocket teeth and the endless double chain is provided.